There have currently been developed in medicine a whole series of imaging systems that can be used to take pictures of the interior of the body of a patient. These include, for example, the magnetic resonance units and radionuclide emission tomography recording devices named at the beginning. Among these are PET systems (PET=Positron Emission Tomography) and SPECT systems (SPECT=Single Photon Emission Computer Tomography), in the case of which small amounts of specific substances provided with radioactive materials, so-called “tracers”, are injected into the human body in order to detect various metabolisms in the body by measuring the radioactive radiation.
The amount of injected material is extremely small and lies in the subphysiological range. Consequently, no influencing of the metabolic process to be examined comes about, nor do toxic reactions occur. The weakly radioactive radiation is registered with the aid of scintillation detectors, and an image is produced therefrom. The tracer accumulates in specific organs and/or tumors, and thus permits a very good diagnosis of the metabolisms and, in particular, a very easy and exact detection of tumors and metastases in the surrounding tissue.
Such methods can also be used, for example, to assess the flow of blood to the cardiac muscle. Whereas in the case of magnetic resonance tomography, it is possible to produce a relatively well spatially resolved image data record in which specific structures, for example specific organs, can be detected particularly well, PET and SPECT systems are, by contrast, used to produce images in which specific pathological changes can be identified. Specifically, an exact identification of metabolisms that indicate a pathological change is not directly possible with the aid of normal magnetic resonance methods. Consequently, both magnetic resonance images and radionuclide emission tomography image data of an examination object are meanwhile being acquired ever more frequently and are being adapted to one another such that they can be superposed in an image in a fashion true to location.
These images, which contain the mutually adapted information from various recording methods are denoted below as examination result images or, for short, as “result images”. Such image fusion methods also exist for images from other image recording devices. Thus, for example, DE 103 57 184 A1 describes a method in which magnetic resonance images of the interior of a hollow organ are superposed on 3D-fluorescence images that have been made with the aid of an instrument to be introduced invasively into the same body region.
The mutual geometric adaptation, required for superposition, of the image data of the individual images, which is usually also denoted as “registration” of the images, requires a substantial outlay on computation. Consequently, it is proposed in US 2006/0004275 A1 that instead of the complete PET and/or SPECT images, on the one hand, and magnetic resonance images, on the other hand, only previously selected image regions of interest, so-called “Regions of Interest” (ROI) or “Volumes of Interest” (VOI), of the respective images or image data records are being registered on one another and are being superimposed. These ROI or VOI are fixed manually by the user with the aid of a graphical operator interface.
There have already currently been developed combined imaging systems that have both a magnetic resonance recording device and a radionuclide emission tomography recording device. However, here, as well, the magnetic resonance images and the radionuclide emission tomography image data are firstly processed completely separately and subsequently superposed. The advantage of these systems resides, however, in that because they have been prepared on the same system, the images are already registered in terms of hardware and thus can more easily be superposed in a fashion true to location.